What exactly is centrifugal force

A.T.

Then I'm sure you will soon have convinced anyone to stop using them. Let us know when all the books have been revised.
It leads to the same quantitative predictions, which is all that matters in physics. The rest is philosophy.

rcgldr

They wouldn't. The net force on each object is inwards. The objects (and the ends of the string) are accelerated "inwards" by the tension in the string. The outwards force exerted by the objects onto the ends of the string is a reaction (to acceleration) force, not a net force, equal in magnitude and opposing the tension at the ends of the string.

sophiecentaur

This thread reads like something out of Gulliver's Travels, actually. Anyone would think that there is some actual 'reality' in it all. People don't acknowledge that Science is the pragmatic business of predicting things - all the rest is faith.

DaleSpam

Just throwing in my 2 cents worth. I agree with A.T. here. Fictitious forces do most things that you expect real forces to do, including do work in the non-inertial frame in which they exist.This can be true in certain circumstances, but it is not generally true.Interesting idea. I was aware of this in terms of gravity in GR, but hadn't thought clearly about the advantage for Newtonian physics also. As we discussed in that other thread, I am not convinced about this because of the double-degeneracy of the metric in Newtonian physics. But I haven't looked at it closely (for that same reason).This is simply wrong. If you look at A.T.'s little astronaut cartoon, suppose that the astronaut is standing on a section of the floor supported by bolts which can be suddenly cut. If they are suddenly cut then the reactive centrifugal force will accelerate the section of the floor away from the center. It is only the presence of the bolt forces which prevents the floor from fleeing the center under the influence of the centrifugal reaction force.

rcgldr

In this situation, there is no reaction force, because there is nothing to exert a reaction force onto. The only forces are gravitational. The only "outwards" force would be exerted onto the surface of the planet, but that force is due to gravity, not a reaction force. In this situation, the reaction to gravitational force is a change in the path of the moons as they orbit.

A reactive force is a response to acceleration of an object wrt inertial frame. In an inertial frame, once the floor is cut, the astronaut and the floor cease to accelerate, so there is no reactive centrifugal force. In a rotating frame, the reactive centrifugal force also vanishes (the astronaut ceases to exert a force onto the floor), and the fictitious centrifugal force now changes in to a combination of fictitious centrifugal and coriolis forces that correspond to an object moving at constant velocity wrt inertial frame, as observed from a rotating frame.

stevendaryl

There are lots of bad ideas that are taught to beginning students of physics that have to be "untaught" to advanced students. Inertial forces is one of them. "Relativistic mass" is another.

It doesn't lead to ANYTHING. Calling something a "force" when it's not is just bad terminology. It's not an alternative approach to doing physics.

stevendaryl

The claim that "Science is the pragmatic business of predicting things - all the rest is faith" is itself a philosophical position, and is therefore, not science.

A.T.

It leads to the same quantitative predictions, which is all that matters in physics. The rest is philosophy.

stevendaryl

Calling something a "force" doesn't lead to ANYTHING. If you think otherwise, give an example of how something follows from the fact that you call certain terms "forces".

stevendaryl

The claim that nothing matters other than quantitative predictions is itself a philosophical claim. It's funny that the people who bring up "that's just philosophy" as an argument are the ones who actually end up making the strongest philosophical claims.

A.T.

...in physics.
The argument is "The rest is philosophy, so there is no point arguing about it on a physics forum".

stevendaryl

But that's basically this entire thread. The physics part is nothing more than:

"If one uses noninertial, curvilinear coordinates, then additional terms appear in the equations of motion."

One sentence. Everything else is an argument for a particular way of looking at those additional terms.

A.T.

All forces are just "certain terms". So I don't see how this is an argument against inertial forces specifically.

stevendaryl

I also want to point out that connection coefficients (the preferred, in my opinion, way to deal with noninertial, curvilinear coordinates) are essential to understanding General Relativity.

stevendaryl

No, they're not. Real forces have certain properties that the fake forces don't:
(1) They are vector quantities, meaning that they exist in EVERY coordinate system. The components change when you change coordinate systems, but a vector is a geometric quantity that is independent of coordinates.
(2) Real forces have corresponding reaction forces, leading to conservation of momentum.

In contrast, "inertial forces" are artifacts of a particular choice of coordinates. They don't have corresponding reaction forces. They can be made to disappear by choosing the appropriate coordinate system.

A.T.

You can easily find examples where reactive centrifugal force pushes things outwards in the rotating frame. Two blocks on a turntable. An outer light one with high friction. An inner massive one on rollers. The inner block applies a centrifugal interaction force to the outer block, which pushes the outer block away from the center in the rotating frame.

But all of that is not relevant to the "centrifugal"-label for the reason I state in post #64.

A.T.

Give an example of how something follows from the fact that you call them "forces".